Conductive plastics can be printed on membranes to create
solar cells in a new technology developed by Princeton researchers with a National
Science Foundation grant.
"Conductive polymers have been around for a long
time, but processing them to make something useful degraded their ability to
conduct electricity," says Yueh-Lin Loo, an associate professor of
chemical engineering at Princeton. "We have figured out how to avoid this
trade-off. We can shape the plastics into a useful form while maintaining high
conductivity."
The Princeton researchers treat the polymers with an acid
to relax them following processing. Electrodes of a transistor were produced by
printing treated conductive plastic onto a surface.
"Being able to essentially paint on electronics is a
big deal," Loo says. "You could distribute the plastics in cartridges
the way printer ink is sold and you wouldn't need exotic machines to print the
patterns."
This method could be used to replace indium tin oxide
(ITO), a conducting material often used in solar panels. The conductive
material is transparent to allow sunlight to pass through to the materials in
solar cells that absorb light energy.
There are some limiting factors with ITO. For one, high
concentration of charge carriers will increase ITO's conductivity, but decrease
its transparency. Another issue is that ITO has been in strong demand for
competing applications, including liquid crystal displays, flat panel displays,
plasma displays, touch panels, electronic ink applications, organic
light-emitting diodes, antistatic coatings and EMI shielding. ITO is used as
the anode in organic light-emitting diodes.
Biomedical
Sensors
Loo says the treated conductive plastics may also be used
for flexible displays and biomedical sensors that would display a certain color
if a person had an infection. The plastics change color when exposed to a
chemical compound common in ear infections.
Other researchers include Joung Eun Yoo, who received her
doctorate in chemical engineering from the University of Texas-Austin in 2009
with Loo as her adviser; Kimberly Baldwin, a high school student who spent a
summer in Loo's lab; Jacob Tarver, a Princeton chemical engineering graduate
student; Enrique Gomez of Penn State University; Kwang Seok Lee and Yangming
Sun of the University of Texas-Austin; Andres Garcia and Thuc-Quyen Nguyen of
the University of California-Santa Barbara; and Hong Meng of DuPont Central
Research and Development.
The research was supported by the National Science
Foundation, the W.M. Keck Foundation and the Arnold and Mabel Beckman
Foundation.
Use of conductive plastics in solar cells is not new.
Design News has previously reported on
commercial projects under way at
Konarka and
Plextronics. The
Princeton research could presumably improve the economics for conductive
plastics in solar applications.
In the 1970s, Alan J. Heeger, Alan MacDiarmid and Hideki
Shirakawa reported high conductivity in oxidized iodine-doped polyacetylene in
research that earned them the 2000 Nobel Prize in Chemistry "for the
discovery and development of conductive polymers." They were part of a
large effort dating back to the 1950s that had explored conductive polymers.
Today a trade group called the
Organic
Electronics Assn. actively promotes commercial applications of
conductive polymers.
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